New Australian research has shown that mixtures of heavy metals and pesticides in contaminated sites can be toxic for much longer than previously thought.

West Australian soil microbiologist Dr Mallavarapu Megharaj is part of a team at CSIRO Land and Water investigating the impact of pollution on micro-organisms, and using the sensitive ones in biological tests (bioassays) for soil and water contamination.

"Current chemical tests for pollution only detect the presence of individual chemicals," he said. "But in reality we see a mixture of contaminants, and these can interact to have serious effects on living organisms."

Dr Megharaj has found, for example, that the heavy metal copper, a residue from many fungicides, can extend the life of the herbicide atrazine by killing off the micro-organisms that would normally break down the chemical.

He has also shown that cadmium, a residue from phosphate fertilisers, kills off soil algae, and will test to see whether it too may extend the life of pesticides in the soil.

"It's important to assess this because the longer a chemical persists in the environment, the more damage it can do," he said.

"Bioassays must be used in conjunction with chemical analysis because they go beyond reporting on just the presence of a chemical, to reveal its bioavailability and biological facts. And these are the factors that matter in terms of risk assessment and remediation."

Dr Megharaj has been the first to use soil algae to measure the total toxicity of a mix of heavy metal and pesticide contaminants, and has found them to be very sensitive.

His team's results were presented at a recent workshop held in Adelaide.

"We found that soil algae were completely eliminated in soil highly contaminated by chromium at Mount Barker in Western Australia," he said.

Dr Megharaj does not agree with the usual method of using aquatic bacteria and algae to bioassay contaminated soil.

"Soil organisms should be used for testing soil contamination," he said.

Surprisingly, he has found that while some soil algae are sensitive pollution indicators, others can actually be used to biodegrade pesticides and accumulate heavy metals. These could be used in bioremediation of sites, although this is generally more practical in water where it is easier to separate and dispose of the algae after they have accumulated the heavy metals.

There are hundreds of thousands of known contaminated sites worldwide, with at least 80,000 in Australia alone. According to Dr Megharaj, many more may have escaped detection due to lack of sensitive biological tests.

His team has also recently isolated a bacteria which degrades the pesticide Fenamiphos and its toxic byproducts.

Fenamiphos is used worldwide to kill nematodes; contamination of soil and groundwater with the pesticide is a major problem.

Dr Megharaj's team has received provisional patent approval for the application of the newly isolated bacteria.